Actually the notation is correct.
A 12/8 time signature contains 4 groups/beats of three quavers/8th notes. Your desired notation represents 6/4.
And according to the common notation convention the staccato articulation is supposed to be placed on the last note of a tied group.
Nevertheless you can force the 6/4 appearance with force duration. Start note input at the first tied note, tap force duration (the c-clamp symbol) select a crotchet/quarter note duration and play the D.